The present invention generally relates to towable devices which are used to grade ground surfaces or spread various materials over the ground surface where it is desirable to obtain a particular finished grade of ground surface or to blend additives into the soil. Such grater-spreader devices are used for a variety of purposes, such as applying paving materials, grading land for construction, and preparing land for agricultural purposes. More particularly, the present invention relates to a grader-spreader adapted to being towed by a tractor having a three-point hitch, where the blades of the apparatus readily adjust to a desired width. An additional feature of the present invention is that the angle and elevation of the cutting blades with respect to the ground surface are readily adjustable, thus allowing the operator to obtain a particular finished grade or slope.
It has been long known that devices towable by tractor provide an efficient and economical means of grading a ground surface and for applying various materials to the ground surface. While self-propelled grading and spreading machinery may accomplish the same task as towable devices, self-propelled machines are expensive, require substantial maintenance, and are often complicated to operate. Because towable devices are propelled by an all-purpose tractor, the devices are relatively inexpensive, simple to operate, and require less maintenance than self-propelled grading and spreading devices.
It has also been a long recognized need that towable grader-spreaders should be adaptable to provide service in a variety of different working conditions. If a grader-spreader device is used in a large open field to prepare the ground surface for planting crops, the operator may desire to adjust the device to obtain a virtually flat surface. However, if the device is used to spread asphalt on a roadway, it is often desired to obtain a final surface with sufficient slope to allow rain and spilled materials to rapidly drain off of the roadway surface.
The invention described in U.S. Pat. No. 4,320,988, issued to Seal on Mar. 23, 1982, discloses a towable grader-spreader utilizing a plurality of cutting blades adjustable in depth and angular position. The patent discloses a device which utilizes a plurality of cutting blades which can function as grader blades or as a spreader. The blades of the invention are adjustable both in depth and in angular position, where the respective ends of the blades may be positioned at different cutting depths from each other so as to vary the angle of a cut on a surface. The blades of the invention are positioned by a hydraulic ram adjustment mechanism. The cutting blades are mounted between a pair of side runners. The width of the device is fixed because the side runners are fixedly attached to one another.
The grader-spreader of U.S. Pat. No. 5,191,943 issued to Minor et al. on Mar. 9, 1993, discloses a pair of transversely extending blades rigidly mounted between two side members. While the ends of the blades of the grader-spreader in the '943 patent are vertically adjustable, the width of the device is fixed.